exception

javax.servlet.ServletException: java.lang.LinkageError: loader constraint violation: when resolving interface method "javax.servlet.jsp.JspApplicationContext.getExpressionFactory()Ljavax/el/ExpressionFactory;" the class loader (instance of org/apache/jasper/servlet/JasperLoader) of the current class, org/apache/jsp/OnDuty/wfmanage_jsp, and the class loader (instance of org/apache/catalina/loader/StandardClassLoader) for resolved class, javax/servlet/jsp/JspApplicationContext, have different Class objects for the type javax/el/ExpressionFactory used in the signature
 org.apache.jasper.servlet.JspServlet.service(JspServlet.java:275)
 javax.servlet.http.HttpServlet.service(HttpServlet.java:717)

root cause

java.lang.LinkageError: loader constraint violation: when resolving interface method "javax.servlet.jsp.JspApplicationContext.getExpressionFactory()Ljavax/el/ExpressionFactory;" the class loader (instance of org/apache/jasper/servlet/JasperLoader) of the current class, org/apache/jsp/OnDuty/wfmanage_jsp, and the class loader (instance of org/apache/catalina/loader/StandardClassLoader) for resolved class, javax/servlet/jsp/JspApplicationContext, have different Class objects for the type javax/el/ExpressionFactory used in the signature
 org.apache.jsp.OnDuty.wfmanage_jsp._jspInit(wfmanage_jsp.java:27)
 org.apache.jasper.runtime.HttpJspBase.init(HttpJspBase.java:52)
 org.apache.jasper.servlet.JspServletWrapper.getServlet(JspServletWrapper.java:159)
 org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:329)
 org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:342)
 org.apache.jasper.servlet.JspServlet.service(JspServlet.java:267)
 javax.servlet.http.HttpServlet.service(HttpServlet.java:717)

原因是项目中WEB-INF\lib中的三个jar包(juel.jar, juel-engine.jar, juel-impl.jar)和tomcat6下lib中jar包(el-api.jar)冲突

解决方法：

方法一：换成tomcat5.5 一点问题也没有了

方法二：将juel.jar, juel-engine.jar, juel-impl.jar这三个包复制到tomcat6下lib中，并删除原来的el-api.jar，切记要把WEB-INF\lib中的juel.jar, juel-engine.jar, juel-impl.jar删除。不然还是要冲突。